A nickel containing hypereutectic aluminum-silicon sand cast alloy is disclosed herein containing 18-20% by weight silicon, 0.3-1.2% by weight magnesium, 3.0-6.0% by weight nickel, 0.6% by weight maximum iron, 0.4% by weight maximum copper, 0.6% by weight maximum manganese, 0.1% maximum zinc and balance aluminum. The alloy may have a more narrow nickel content of 4.5%-6.0% by weight, and up to 2% by weight cobalt. The alloy may be substantially free from iron, copper and manganese. The alloy of the present invention is preferably sand cast, and most preferably lost foam cast with a pressure of 10 ATM to produce engine parts with high thermal properties that are easily machined.